Diamond Blackfan anemia (DBA) is a congenital anemia that presents in children, often before one year of age (Vlachos et al., 2008). The primary symptom for these patients is a block in erythroid differentiation and possible defect in hematapoietic stem cells (HSCs), and some patients also have craniofacial anomalies. Ribosomal protein S19 (RPS19) was the first gene found mutated in DBA patients (Draptchinskaia et al., 1999). Sequencing of patient samples has identified mutations of either large (60s) or small (40s) subunit ribosomal proteins in over 50% of patients (Vlachos et al., 2010), most recently rps29. Patients are heterozygous for these mutations, always maintaining a wildtype copy of the affected ribosomal protein gene.
Ribosomal protein knockdown leads to an increase of free ribosomal proteins. Some ribosomal proteins, including RPL11 and RPL5, can prevent p53 degradation, as they are able to bind MDM2 and sequester it from p53 (Fumagalli et al, 2009). RPL26 has been shown to increase p53 protein by an alternative mechanism, as it can bind p53 mRNA, increasing its translation (Tagaki et al., 2005). p53 activation plays an important role in DBA pathogenesis, as well as in other diseases where ribosomal and related genes are mutated, now termed ribosomopathies. These include 5q-myelodysplastic syndrome, where one copy of RPS14 is lost. p53 activation is also a common feature in bone marrow failure disorders, such as Fanconi Anemia (Ceccaldi et al., 2012). In human CD34+ cells, RPS19 knockdown leads to p53 activation (Ebert et al., 2005; Flygare et al., 2005), with increased accumulation in erythroid cells. Differentiation defects can be rescued by p53 inhibition (Dutt et al., 2011). Mouse models of RPS19 mutation or knockdown have hematopoietic defects that can be rescued by p53 mutation (McGowan et al., 2008; Jaako et al., 2011). Rps19 has been targeted by morpholino in zebrafish embryos, and the hematopoietic defects in rp111 mutant zebrafish are rescued by p53 knockdown (Danilova et al., 2008; Torihara et al., 2011; Danilova et al., 2011).
Ribosomal protein mutations are common in patients with Diamond Blackfan anemia (DBA), who have red cell aplasia and craniofacial abnormalities. The inventors have previously characterized zebrafish mutant rps29, a ribosomal protein in the small subunit, that have hematopoietic and endothelial defects (Taylor et al., 2012). Rps29−/− embryos have morphological defects in the head, as well as decreased hematopoietic stem cells, hemoglobin, and staining of endothelial markers. Consistent with other models of DBA, knockdown of p53 near completely rescues the rps29 mutant phenotype.
The inventors demonstrated that Rps29−/− embryos have a defect in arterial specification, leading to decreased HSCs and decreased flk1 expression in the intersegmental vessels at 24 hours post fertilization (hpf). Primitive erythropoiesis is also affected, as rps29−/− embryos have less hemoglobin. These embryos also have increased apoptosis, particularly in the head, and die by five days post fertilization (dpf). p53 pathways are activated in the embryo, and p53 mutation rescues all hematopoietic and apoptotic phenotypes.
The current treatment options for diseases associated with a ribosomal disorder or ribosomopathy, e.g., a mutation in a ribosomal protein are far from optimal, especially for Diamond Blackfan anemia (DBA). As such, it is imperative to discover novel, effective, and targeted therapies for these diseases associated with a ribosomal disorder or ribosomopathy, e.g., a mutation in a ribosomal protein. In particular, there is a strong need in the art for improved methods for treatment of DBA with small-molecule drugs.